Withy Cottage

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Timber Frame & Straw Bale self build with thermal bridge free construction (other than door and window frames). Simple flat raft foundation on EPS.
Images Graphs Figures Description Strategies Building

Withy Cottage : Project images

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CO2 emissionsPrimary energy requirement
Energy target
Superinsulation design in 1995

Energy and fuel use

Fuel use by type
Primary energy requirement
CO2 emissions

Measured data from renewable generation is not yet available.

Fuel use

Electricity use - - 1528 kWh/yr
Natural gas use- - -
Oil use- - -
LPG use- - 600 kWh/yr
Wood use- - 8000 kWh/yr
Other Fuel - - -
Primary energy requirement - - 111 kWh/m².yr
Annual CO₂ emissions - - 10 kg CO₂/m².yr
Annual space heat demand - - -

Renewable energy

Electricity generationForecastMeasured
Renewables Technology--
Other Renewables Tech--
Electricity consumed by generation --
Primary energy requirement
offset by renewable generation
-111 kWh/m².yr
Annual CO₂ emissions
offset by renewable generation
-10 kg CO₂/m².yr

Calculation and targets

Whole house energy calculation method
Other whole house calculation method-
Energy target Superinsulation design in 1995
Other energy targets-
Forecast heating load 60 W/m² demand


Pre-development air permeability test03 January 20061.38m³/m².hr @ 50 Pascals
Final air permeability test--

Project description

Start date24 December 2004
Occupation date
Location Hereford Herefordshire  England
Build typeNew build
Building sectorPrivate Residential
Property typeDetached
Construction typeOther
Other construction typeTimber with staw wall insulation and blown celulose insulation
Party wall construction
Floor area 120
Floor area calculation method Approximate Floor Area
Building certification

Project Team

Project lead person
Landlord or ClientSelf
Mechanical & electrical consultant None
Energy consultantNone
Structural engineerAlan Pearce
Quantity surveyorNone
Consultantfriends informal chats
ContractorSelf plus Mike Whitfield, Dai Rees (el) and Steve Rann (plaster)

Design strategies

Planned occupancy2 people plus guests
Space heating strategySingle woodstove with domestic hot water back-boiler. Towel rail in bathroom as heat dump otherwise no radiators, secondary heaters or other heat emitters.
Water heating strategySolar and woodstove compliment each other with very infrequent immersion heater backup.
Fuel strategyWaste wood from local sawmill and timber from on-site woodland management. LPG hob and electric oven.
Renewable energy strategyDisconnected after 7 years living off the grid. Emphasis on demand reduction.
Passive Solar strategyDIY Solar thermal DHW, minimal passive solar because of uninformed fear about overheating in lightweight building. In fact behaves like a massive building due to insulation.
Space cooling strategyControled gains, night ventilation and high levels of insulation maintain very comfortable summer temperatures (peak summer temperatures 23-24C)
Daylighting strategyNot optimised. Open plan living area with light from at least 2 sides in all rooms. One skylight in office and one in kitchen/dining/living area. Emphasis on animation and effect rather than DF.
Ventilation strategySimple passive stack cooker hood and thru' wall MVHR in bathroom. Trickle vents in office and bedrooms. Considering MVHR retrofit.
Airtightness strategy Internal structure, 9mm ply air barrier behind 100mm structure/services layer. Continuous air barrier but unaware of proper airtightness tapes at time of build. Blower door tested after completion.
Strategy for minimising thermal bridges Floating slab on 100mm EPS with 200mm edge insulation. Structure inside the insulation with rafters and gable support outside insulation layer. However windows and doors are major thermal bridge.
Modelling strategyBasic spread sheet.
Insulation strategyEPS under slab, local straw bales for walls and blown cellulose in roof.
Other relevant retrofit strategies
Contextual information

Building services

Occupancy2 plus guests
Space heatingWood stove only
Hot waterSolar plus wood stove back boiler (1kW)
VentilationCrude passive stack and trickle vents plus single room MVHR in bathroom.
ControlsNone except thermostat on thermal store to dump heat to bathroom tower radiator if too hot.
CookingLPG and electric oven
LightingAll CFL, linear T5 or LED spots. No incandescents.
AppliancesAll best available at time of purchase.
Renewable energy generation systemSolar DHW
Strategy for minimising thermal bridgesContinuous layer of insulation with structure on inside. Floating floor slab with no penetrations.

Building construction

Storeys 2
Volume -
Thermal fabric area -
Roof description 15mm plasterboard and skim, Self built 400mm truss rafters with cellulose insulation between, breather membrane, 50mm air gap, 18mm ply, MDPE membrane, 150mm turf from site.
Roof U-value 0.11 W/m² K
Walls description 12mm plasterboard and skim, 100mm service void in structural frame, 9mm ply air barrier, straw bales stacked up in thin orientation, breather membrane, air gap, douglas fir cladding.
Walls U-value 0.20 W/m² K
Party walls description n/a
Party walls U-value 0.00 W/m² K
Floor description polished concrete on 100mm EPS with 200mm edge insulation. Was seen as a lot of insulation at the time!
Floor U-value 0.19 W/m² K
Glazed doors description Self build by friend, oak frame and double glazed (IPlus with Argon and thermix spacer)
Glazed doors U-value - -
Opaque doors description Self build by friend, Oak, PU foam, birch ply air barrier.
Opaque doors U-value - -
Windows description Ecoplus stormproof with iPlus glazing.
Windows U-value - -
Windows energy transmittance (G-value) -
Windows light transmittance -
Rooflights description 2 x Velux with best available glazing at the time.
Rooflights light transmittance -
Rooflights U-value -